Bad breath after brushing may be caused by oral diseases, gastrointestinal diseases, pharyngeal or tonsillar diseases. 1. Oral disease: usually if the patient suffers from periodontitis and other oral diseases, one of the more common symptoms is bad breath, in addition may also be accompanied by bleeding, gum recession and other symptoms. 2. Gastrointestinal diseases: If the patient suffers from gastroesophageal reflux disease (GERD), the stomach contents will retrograde from the esophagus, resulting in bad breath after brushing the teeth. In addition, patients with Helicobacter pylori infection may also have bad breath. 3. Pharyngeal or tonsil disease: If the patient suffers from pharyngitis and tonsil inflammation and other respiratory diseases, bad breath may occur at the same time and accompanied by pharyngeal or tonsil pain and other symptoms. There are many other reasons why your mouth still smells bad after brushing your teeth, so it is recommended that patients actively seek medical attention to clarify the cause of the disease and standardize the treatment.